Nothing Says Yes Like NO, to Eggs

Science's STKE  15 Aug 2000:
Vol. 2000, Issue 45, pp. tw7
DOI: 10.1126/stke.2000.45.tw7

It is well known that Ca2+ fluxes occur before the activation of the fertilized ovum; however, little is known about the events preceding Ca2+ mobilization. Kuo et al. show that nitric oxide (NO) is required for egg activation. Fluorescence assays indicated that NO synthase is present in sperm at the head and concentrated at the acrosome; however, NO production depended on the acrosome reaction. Eggs injected with a NO donor, S-nitrosoacetylpenicillamine (SNAP), or with recombinant NO synthase in conjunction with calmodulin became activated, whereas preinjection of eggs with oxyhemoglobin (oxyHb), a NO scavenger, prevented egg activation. Addition of ionomycin to oxyHb rescued the ability of eggs to become activated. Similarly, injecting SNAP into eggs elicited a strong wave of Ca2+ release; this was blocked by preinjection with oxyHb, suggesting that NO production is necessary and sufficient before the elicitation of Ca2+ fluxing and egg activation.

Kuo, R.C., Baxter, G.T., Thompson, S.H., Stricker, S.A., Patton, C., Bonaventura, J., and Epel, D. (2000) NO is necessary and sufficient for egg activation at fertilization. Nature 406: 633-636. [Online Journal]